The Wisconsin Ultraviolet Photo-Polarimeter Experiment

Most of the light we encounter every day is a chaotic mixture of light
waves vibrating in all directions. Such a combination is known as unpolarized
light. However, if the light -- or other type of electromagnetic energy --
passes through certain materials or is reflected, the waves will tend to
vibrate in one direction and the light is said to be polarized. You can
observe polarized light by looking through a pair of polarizing sunglasses
at the brightness of the blue sky about 90 degrees from the Sun. As you
rotate the glasses, the brightness of the sky will vary because the light
has been polarized by being reflected in the atmosphere.

By determining the amount and direction of polarization and how these change
with wavelength, one can learn about what causes the energy to become
polarized. By using polarimetry (the study of polarization), scientists
can learn a great deal about the object being observed and the space
between the object and Earth.

The Wisconsin Ultraviolet Photo-Polarization Experiment science program is
the first and most comprehensive effort to exploit the unique powers of
polarimetry at wavelengths not visible on Earth. To do this, the telescope
has a 50-centimeter (20-inch) mirror to reflect ultraviolet light to a
spectropolarimeter, which measures the degree and direction of polarization
at many different wavelengths. Before the development and flight of this
experiment on the Astro-1 mission, virtually no such data existed because
of the difficulty in obtaining these measurements with the degree of
accuracy required for astronomical observations.

During the Astro-1 mission, the Wisconsin Ultraviolet Photo-Polarimeter
Experiment team observed a variety of astronomical objects including the
interstellar medium, hot stars, and active galaxies. The data gathered have
allowed astronomers to refine theories and develop a better understanding of
the universe. Many of these same types of objects will be observed in more
detail during the Astro-2 mission to further improve our knowledge of the
cosmos.